The simplest way is to use Chartio's Combine Columns Data Pipeline step.
If you'd like to customize how the columns are combined, you can do so with a custom formula.
Chartio's Data Pipeline recognizes standard SQLite expressions. This means you can use the || operator, which allows you to concatenate (combine) values.
Click the +Add Step button in the Data Pipeline, and then choose Add Column from the dropdown menu. Label your column. In the Formula input, add || between the values you want to concatenate.
If you want to hide any of your original columns, add a Hide Columns step in the Data Pipeline after the Add Column step.